Climate change

Climate change is one of the most important drivers of current and likely future change in global ecosystems. Increasing temperatures, changes in patterns of precipitation and altered weather patterns are likely to have damaging impacts on biodiversity for the most part, although some species in some parts of the world may benefit. Species are expected to move away from their traditional areas as our climate changes to find new locations with suitable climate and habitat, which could lead to declines in numbers or loss of populations if new favourable areas are not available or species are unable to move. Changes in the timing of when species breed, move to wintering sites or when their food is available may also have impacts on populations.

Climate change in the UK

In the UK, our climate has already shown signs of change over the last 100 years, with an increase of 1 degree C in central England during that period, for example (Hulme et al. 2002). The trends of overall increasing temperature, increasing winter precipitation and decreasing summer precipitation are expected to continue. Average annual UK temperatures are predicted to increase until the 2080s with an earlier onset of spring and a later onset of winter. Average annual precipitation is likely to decrease overall but with wetter winters, drier summers and more frequent periods of extreme weather (Hulme et al. 2002). Climate change has an impact on our biodiversity.

Impacts of climate change on bats

So how might climate change affect bats in the UK? Bats may be affected at all stages in their annual cycle: temperature changes may affect hibernation of bats, both in terms of the availability of suitable sites and behaviour, length and timing of hibernation. Changes in temperature and precipitation may affect breeding success of female bats through changes in prey availability, including the time of year when insects are abundant. Climate change may also affect the habitat types and insect prey types available for bats for foraging, which could have indirect effects on bat populations. The distribution of UK bat species may also change in response to climate change.

To date there is some evidence that climate has had an impact on our horseshoe bats. It is likely that the very cold winters in the second half of last century reduced population sizes of horseshoe bats, but it has been suggested that more recently the mild winters have allowed populations of both lesser and greater horseshoe bat to recover (Ransome 1989; Battersby 2005). Spring temperature is also important for some bat species: greater horseshoe bat numbers increased after a period of warm springs for example (Ransome & McOwat 1994) and the timing of births is influenced by spring temperatures in pipistrelles (Racey & Swift 1981) and greater horseshoe bats. However we don’t yet know enough to determine whether reproductive success of bats is directly related to climate or to the availability of their insect prey (which may also be affected by climate) and it is possible that there could be mismatches between timing of breeding and the availability of food, particularly for specialist species of bat reliant on particular prey types (Rebelo et al. 2010). Also bats may emerge from hibernation earlier in the year if spring temperatures are higher and then could be at risk from mortality during subsequent cold periods (Jones et al. 2009).

As temperatures increase with climate change, shifts in or expansion of species' ranges are expected to be in a northerly direction or to higher elevations. Some UK bat species reach the northern limit of their range in the UK and are predicted to expand northwards in the future (Rebelo et al. 2010). However, this assumes that there will be suitable roosts and habitats available and that the bats are able to disperse successfully into new areas. Dispersal may be more likely for bat species than other mammals due to their ability to fly and for some species, to migrate. The extent of bat migration in the UK is not well documented but it is likely that most bat species in the UK are less migratory than in continental Europe where long distance migrations have been recorded for a number of species (Hutterer et al. 2005). There is evidence that one species, the migratory Nathusius’ pipistrelle may already be showing a range response to climate change. Records for this species have increased in recent years, and its recorded range expansion in the UK matches that predicted by changes in climate over the last few decades (Lundy et al. 2010).

More research and ongoing monitoring of population change is needed before we can fully understand how bat species will be impacted by the future predictions of climate change in the UK.